There are many instances where compressed audio-video (A/V) information is transmitted or stored and must be played back by a “legacy” decoder (i.e., a decoder using an earlier standard). Such systems often allow for the transmission or storage of related non-A/V data such as closed captioning information.
It would be desirable to have additional capability for the transmission and/or storage of related non-A/V data (e.g., private and/or enhancement information) with compressed audio and/or video bit streams that (a) can be processed by decoding devices that are aware of the possible presence of the data and (b) will not affect legacy decoders that cannot process the data.